Various epoxy compounds such as α-pinene oxide, limonene oxide, and styrene oxide are important intermediates in the production of chemical products such as flavoring agents. Also, alicyclic epoxy compounds such as β-pinene oxide and camphene oxide are substances important as, for example, encapsulants for electronic materials and cationically curable resins.
As methods for producing such epoxy compounds, patent literature 1 discloses a method for epoxidizing an alicyclic compound having a carbon-carbon double bond by reaction with a percarboxylic acid; and a method for epoxidizing an alicyclic compound having a carbon-carbon double bond by reaction with hydrogen peroxide in the presence of a solvent and a catalyst such as an osmium salt or tungstic acid. However, the former method is problematic in that, for example, peracids are compounds that require careful handling because they are, for example, explosive, and equimolecular wastes are generated after reaction. The latter method is preferable in that hydrogen peroxide generates only water as a by-product but problematic in that the osmium salt is highly toxic.
Patent literature 2 describes a method for producing styrene oxide in which styrene is reacted with peracetic acid in the presence of an alkali metal salt of a weak acid. This method, however, has a problem in that peracetic acid is a compound that requires careful handling because of its explosibility and like properties.
Patent literature 3 describes a method for producing styrene oxide in which styrene is reacted with hydrogen peroxide in the presence of arsenic oxide and 3,5-di-tert-butyl-4-hydroxytoluene. This method, however, is problematic in that arsenic oxide is highly toxic.
Patent literature 4 describes an epoxidizing method in which an alkene such as styrene, indene, cyclohexene, or α-pinene is oxidized by hydrogen peroxide in water or in water and an organic solvent in the presence of a transition metal salt such as manganese sulfate or cobalt acetate, an inorganic promoter such as sodium bicarbonate, and an organic co-promoter such as urea. This method, however, is disadvantageous in that since the method is performed under high dilution conditions, the efficiency for using hydrogen peroxide is poor, and industrial productivity is inferior.
Nonpatent literature 1 describes a method for epoxidizing a terpene such as limonene in an organic solvent such as acetonitrile using a solid catalyst that was prepared by supporting a tungstophosphoric acid derivative represented by PW4O24[(C4H9)N]3 on an ion-exchange resin in the presence of hydrogen peroxide; and a method for epoxidizing α-pinene, 3-carene, 1-phenyl-1-cyclohexene, indene, and the like by hydrogen peroxide in an organic solvent such as benzene using a tungstophosphoric acid derivative represented by PW4O24[(C8H17)3NCH3]3 and aminomethylphosphonic acid as catalysts. However, these methods are problematic in that it is difficult to produce tungstophosphoric acid derivatives and aminomethylphosphonic acid that serve as catalysts.
Nonpatent literature 2 describes a method for epoxidizing olefins such as cyclooctene, cyclohexene, and styrene; and monoterpenes such as α-pinene, limonene, and 3-carene, in a mixed solvent of dichloromethane and acetonitrile, using a Lewis base adduct of a methyltrioxorhenium, by hydrogen peroxide. Nonpatent literature 3 describes a method for epoxidizing styrene, cyclohexene, cyclooctene, and the like by hydrogen peroxide in dichloromethane using methyltrioxorhenium and pyrazole as catalysts. These methods, however, are disadvantageous in that the catalyst methyltrioxorhenium is very expensive and it is difficult to use it in industrial production.
Nonpatent literature 4 describes a method for epoxidizing styrene, cyclooctene, limonene, and the like by hydrogen peroxide in dichloroethane and acetonitrile in the presence of a manganese-porphyrin complex and imidazole. However, it is problematic to industrially carry out this method since an expensive manganese porphyrin complex is used as a catalyst.
Nonpatent literature 5 reports a method for epoxidizing caryophyllene, which has an exomethylene portion, using highly oxidizing m-chloroperbenzoic acid. This method, however, has a problem in that m-chlorobenzoic acid is discharged as a by-product in an amount equimolar to m-chloroperbenzoic acid.
Nonpatent literature 6 reports a method for epoxidizing longifolene, which has an exomethylene portion, by ozonolysis. This method, however, is problematic in that it is industrially difficult to supply ozone at a specific level and after-treat the side product.
Nonpatent literature 7 discloses a method for epoxidizing olefins such as 1-octene, cyclohexene, 2,4,4-trimethyl-2-pentene, and styrene by hydrogen peroxide using quaternary ammonium tetrakis(diperoxotungsto)phosphates as epoxidation catalysts. Although this method performs the reaction in a heterogeneous system that uses benzene or 1,2-dichloroethane as a reaction solvent that is not miscible with water in order to inhibit hydrolysis caused by water generated from hydrogen peroxide, hydrolysis is not sufficiently inhibited. In addition, benzene and the like are toxic and their industrial use is not preferable.
Furthermore, nonpatent literature 8 discloses a method for epoxidizing 1-octene, cyclooctene, a styrene derivative, and the like using hydrogen peroxide in the presence of sodium tungstate, (aminomethyl)phosphonic acid, and methyltrioctylammonium hydrogensulfate. This method, however, is problematic in that it is difficult to obtain (aminomethyl)phosphonic acid and methyltrioctylammonium hydrogensulfate on an industrial scale.
As discussed above, none of the conventionally known methods for epoxidizing organic compounds having a carbon-carbon double bond is regarded as industrially advantageous in terms of safety and economy.